This invention relates to a method and apparatus for controlling the tension of a closed loop of recording tape moving at high speed through a master tape transporter. This apparatus, generally known as a master tape transport, provides for high speed production of recorded tapes for cassettes and/or eight-track cartridges but can be used for other media as well. In the embodiment of the invention disclosed in this application, the master tape transport operates at a tape speed of 240 ips (6.1 m/sec) and controls any number of slave transports which produce large reels of cassette tape onto which is recorded a large number of replications, ("albums") of the signal conveyed from the master tape transport. The master tape transporter utilizes a closed loop of recording tape which is passed across a pick-up head where a signal on the tape is picked up and conveyed downstream to the slaved duplicators. The loop of tape is conveyed from the pick-up head of the transporter into a bin for accumulation and storage. The tape accumulates in the bin in the form of a loosely packed series of small loops. The tape is pulled from the bin and back across the pick-up heads repeatedly, with each complete circuit of the master tape creating a single "album" on the reel of tape located at each slaved duplicator.
As is apparent, tape moving at such a high speed is subject to a number of tension variations induced by movement of the tape through the air and contact by the tape with various moving and stationary machine surfaces. Variations in tension create random speed variations and misalignments of the tape with the pick-up heads, all of which result in less than adequate reproduction quality in the recordings produced at the slaved duplicators. Tension variations having a particularly significant amplitude are produced as the closed loop of tape is pulled from the storage bin. The weight of the tape, the distance the tape must travel and the friction of the tape moving past other loops of tape in the bin all create significant tension variations which are very difficult to compensate for. In the prior art, these tension variations have been reduced by passing the tape between a capstan and a capstan idler, the tension on which is adjustable to provide a predetermined mechanical hold-back. Operating experience has shown that the hold-back tension required under prior art devices sufficient to achieve an even marginally acceptable level of tension control results in excessive wear of the pick-up heads and other tape-contacting surfaces, and the tape itself. Increase in wear is due to the need of adjusting the average tension higher. This is to ensure the minimum tension during operation is at least high enough for good reproduction. Therefore, problems with prior art methods of high speed tape duplication involve not only poor quality of the end product, but frequent repair and/or replacement of equipment and master tapes.
The problem has become more critical in recent years as audio tape cassettes have become more sophisticated. Wow, flutter, frequency drop-outs and other defects which might not have been noticed on earlier, more primitive cassette players are now obvious when played on modern, state-of-the-art players.
It is therefore imperative to improve the quality of cassette recording and manufacture to a significant degree to take advantage of the higher quality playback results which can be achieved in modern cassette players. Furthermore, audio cassettes are now being challenged in the marketplace by "compact disc" technology which is based on digital rather than analog recording and reproduction, and therefore not susceptible to many of the potential variations which apply in the manufacture of audio cassettes.
The most obvious way to improve tape recording quality and machine and master tape life is to substantially reduce duplicating speeds. However, this is not economically practical. In fact, higher, not lower, productivity and quality is necessary if the technological life of audio cassette recording and manufacturing is to be extended in the face of newer technologies such as compact discs.
This invention achieves for the first time a means by which tension and speed variations can be reduced by a substantial degree thereby improving recording quality, machine and master tape life significantly. The improvement in tension control is achieved by using a vacuum column as a "buffer" whereby downstream speed and tension variations are substantially altogether eliminated. Of course, vacuum columns have been used in tape drives, winders and similar devices for many years. However, the vacuum columns are used strictly as bin buffers to hold a supply of tape during stop/start transitions and to permit the very rapid stoppage or reversal of tape movement without breaking of damaging the tape. This is particularly true in computer tape drives where vacuum columns have been used for many years to permit very rapid location of data on reels of computer tape by frequent and rapid stopping, starting and reversing of tape movement.
However, insofar as is known, a vacuum column has heretofore not been used as a means of achieving precise tension control of a tape moving at a constant, high rate of speed. Surprising results have been achieved by adapting vacuum column technology for use as a means of precise regulation.